Internet Protocol (IP) based applications for cellular devices are emerging and are expected to increase in popularity with the growth of UMTS, EDGE, HSPDA and other telecommunication protocols. A cellular device communicates with the network, and other devices connected thereto, over a wireless connection via a base station or access point. IP-based applications available to cellular devices include ones that enable access to email on remote servers and Instant Messaging, for example, among numerous other functions. Unfortunately, because many applications currently available for cellular devices were designed originally for fixed networks, and then applied to “Wi-Fi” (IEEE 802.11) and then further extended to cellular devices also, they are not necessarily optimized for IP connectivity in a cellular network. This can lead to unacceptable reductions in battery lifetimes for cellular devices, deterring consumers from adopting the applications.
A significant drain on battery capacity is attributable to the wireless connection remaining in an active or “listening” state (“airlink open”), and thus power being consumed by the cellular device, for several seconds following a transmission in either direction over a cellular network. The present inventor has realized that this represents a particularly large overhead when relatively small data packets are to be transmitted frequently, as is typical of the types of data messages associated with various IP-based applications. Modern cellular devices and networks support IP connectivity, for example networks based on GPRS, CDMA-2000 and UMTS technology, in addition to circuit switched voice calls, as carried by GSM and CDMA systems. The cellular network protocols have been designed and optimized for circuit switched voice calls, and not for the “always on” IP connectivity that has been added later. With recurring IP access, network transmitters and receivers are in active states for a much longer time than when they carry only voice calls. This causes a significant drain for battery-powered devices.
The following example is given as an illustration of the relative figures involved, but is not necessarily representative of any specific device. For the purposes of this example, the following assumptions are made: it concerns a cellular device with a battery capacity of 1000 mAH; the device consumes 5 mA during idle time; 100 mA when receiving data (that is, when the airlink is open); and consumes 500 mA when transmitting data (also when the airlink is open). This gives an idle time of 200 hours and a talking time of 2 hours, which is within the parameters of current cellular telephone handsets.
In current wireless communication networks, cellular devices keep the airlink open for about 3 to 10 seconds or so after every data burst that is transmitted or received. The inventor has realized that, consequently, following every transmission or reception of data, of whatever size, the cellular device consumes an additional 100 mA for about 3 to 10 seconds.
Many applications using IP communications involve sending small amounts of data periodically. Some examples of such applications are Instant Messaging (IM), checking for new emails, clients using keep-alive messages and clients supporting “Presence” updates, amongst others, this list not being exhaustive but merely exemplary concerning the type of applications where small amounts of data are transferred. For example, where a user is engaged in an IM conversation and types a message every 5 seconds, it is possible that the airlink may remain open during the entire IM conversation.
An estimate of the effect on battery time of these small data message transmissions is now made to give a comparison with the potential maximum battery lifetime of 200 hours for the example mentioned above. Firstly, assuming that the airlink is kept open for 3 seconds, where data messages are exchanged every 10 minutes, this gives a battery lifetime of 167 hours. Where data messages are exchanged every minute, this leads to a battery lifetime of only 68 hours. An even more dramatic effect occurs if the airlink is kept open for 10 seconds. In this case, the exchange of messages every 10 minutes decreases battery lifetime to 141 hours, and exchanging messages every minute gives a battery lifetime of only 39 hours. Thus, frequent network access may decrease battery lifetime by as much as 80%, in the worse case, but more probably by 24 hours or greater. Not only is this inconvenient and undesirable for consumers, it may also inhibit the introduction of new IP services altogether.